Laser Synthesis and Luminescence Properties of SrAl2O4 ... - CSIC

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greenish emission is attributed to Eu 2+ located inside the host lattice. The width of the bands confirms this result as it is due to the splitting of the mixed 4f5d state by the crystal field of the host lattice. Furthermore, no emission peaks in the red region from the characteristic intraconfigurational transition 4f → 4f of Eu 3+ have been detected, indicating that the rare earth ions that have not diffused remain as divalent europium ions in the grain boundaries. Here, their concentration is so high in comparison to the reduced area of grain boundaries, that the emission from these Eu 2+ ions could be largely quenched, resulting in shorter lifetime values than those corresponding to Eu 2+ ions located inside the grains. On the other hand, the wavelength of the emission band does not vary from SrAl2O4:Eu 2+ to SrAl2O4: Eu 2+ , Dy 3+ . The luminescent centers are Eu 2+ ions, and no additional emission band assigned to Dy 3+ is found in SrAl2O4: Eu 2+ , Dy 3+ . As expected, only the phosphors co-doped with Dy 3+ exhibit significant long- lasting afterglow properties. 2 Decay curves of the afterglow of SrAl2O4:Eu 2+ and SrAl2O4: Eu 2+ , Dy 3+ samples at room temperature are depicted in Fig. 10. The luminescence decay process of the samples is nonexponential. Both decay processes of luminescence undergo an initial fast decay (not shown), followed by a slow decaying process which accounts for the observed long-lasting phosphorescence. The fast decay process corresponds to the intrinsic lifetime of Eu 2+ . The slower decay process, which is significant only in SrAl2O4: Eu 2+ , Dy 3+ samples, is attributed to the presence of Dy 3+ ions into the host lattice. The measured luminescent properties of the phosphors synthesized by this novel laser melting method can be explained in terms of the thermally-activated hole trapping and detrapping mechanism proposed by Matsuzawa et al. 2,31 Based on it, the Dy 3+ ions act as deep hole trapping centers. Upon UV-light exposure, Eu 2+ excitation occurs as a
esult of the electron transition from 4f to 4f5d state, leading to a hole at the 4f ground state level which is thermally released to the valence band at room temperature. The released hole migrates through the valence band until Dy 3+ traps it, so it is assumed that Eu 2+ is converted into Eu + and Dy 3+ into Dy 4+ . When UV excitation ends, the reversed route and the recombination of holes and electrons occurs leading to the measured bright and long-lasting phosphorescence. 4. Conclusions A laser melting method is described for the efficient synthesis of strontium aluminates with the composition SrAl2O4 and related phosphors. The phosphors obtained by this method present the appropriate monoclinic phase structure, with a satisfactory fit for good luminescent properties. The advantages of this method over conventional methods include fast material synthesis in the absence of reducing atmospheres and simple precursor preparation. This versatile laser zone melting method may thus enable the synthesis of other phosphors and a whole plethora of other functional oxides and inorganic materials. Acknowledgments The authors acknowledge financial support from the Spanish Ministry of Science and Innovation (MICINN, projects CEN-20072014 and MAT2010-19837-C06- 06), IMPLASER 99 S.L.L. (www.implaser.com), and the regional Government of Aragón (Spain, project PI119/09, and Excellence Research Groups Program T87). References
Page 1 and 2: Laser Synthesis and Luminescence Pr
Page 3 and 4: Dy 3+ phosphors have replaced the p
Page 5 and 6: according to the nominal compositio
Page 7 and 8: SrAl2O4 has hexagonal and monoclini
Page 9: liquid, molten state, inducing subs
Page 13 and 14: 9. Peng T, Huajun L, Yang H, Yan C.
Page 15 and 16: 24. Gurauskis J, Lennikov V, de la
Page 17 and 18: laser melting. Accumulation of heav
Page 19 and 20: Fig. 2. SrAl2O4: Eu 2+ , Dy 3+ phos
Page 21 and 22: Fig. 4. DSC plot obtained for a SrA
Page 23 and 24: Raman Intensity (arb. units) 100 20
Page 25 and 26: Fig. 8. SEM micrograph of unpolishe
Page 27: Fig. 10. Decay curves of luminescen

Laser Synthesis and Luminescence Properties of SrAl2O4 ... - CSIC

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